Hexerocyclic hydroxy compounds



Patented Feb. 15, 1938 UNITED STATES PATENT OFFICE Eduard Tschunkur,

(lologne-Mulheim, Germany, assignors to I. G. Farbenindustrie Aktiengesellschaft, Frankfort-on-the-Main, Germany No Drawing. Application October 5, 1934, Se-

rial No. 747,090. In Germany October 12,

4 Claims.

The present invention relates to a process for the manufacture of heterocyclic hydroxy compounds, more particularly it relates to compounds which may' be represented by the probable general formula:

wherein stands for sulfur or oxygen.

In accordance with the present invention heterocyclic hydroxy compounds of the above identified formula are prepared by starting with a sulfonic acid of the general formula:

wherein a: means the same as stated above, or a salt thereof, especially a water soluble salt, such as an alkali metal salt, and treating the same with a saponifying agent. The reaction proceeds in such a manner that the sulfonic acid group is saponified with a splitting off of sulfurous acid. As saponifying agents suitable for carrying out the process there come into consideration all the agents known in the art for performing saponification; for example, there can be used acid saponifying agents, such as diluted aqueous mineral acids, for example, hydrochloric acid, sulfuric acid, phosphoric acid and the like, further acid salts, such as bisulfate and the like. Like wise the process can be performed with the aid of an alkaline saponifying agent, dilute aqueous caustic soda lye or aqueous caustic potassium lye being enumerated by way of example.

The conditions of working, i. e. temperature and concentration of the saponifying agent, depend to a high degree on the specific heterocyclic sulfonic acid which is subjected to the reaction and to the specific saponifying agent used. Thus, for example, when subjecting an oxazole-Z-sulfonic acid to our new process, there can be generally applied moderate conditions, while in case of thiazole sulfonic acids generally stronger conditions, such as the application of an aqueous mineral acid, say of about 1 to strength, and higher temperatures, say between about 50 and about 100 C., are preferable. Quite generally,

when using strong saponifying agents, such as.

dilute aqueous mineral acids, say of from about l to about 5% strength, the saponification can erally require higher temperatures, say from about 50 to about 100 C. It is to be understood that the statements hereinbefore made with regard to the concentration and temperature are in no Way limitative and that the conditions of working may be varied in any suitable manner without departing from the spirit of our invention.

The sulfonic; acids used as starting components in our invention are obtainable, for example, according to the process described in the application for Letters Patent Serial No. 723,611, filed May 2, 1934 and having the title Heterocyclic sulfonic acids and process of making same, by reacting upon the corresponding Z-mercapto derivatives, favorably in an alkaline medium, with an oxidizing agent in a quantity corresponding to at least 3 atoms of active oxygen for each atom of the 2-mercapto derivative. Further these sulfonic acids are obtainable by reacting upon compounds of the formula:

arylen C-Cl wherein as means the same as stated above, with a sulfite.

It is self-understood that in performing our new process it is not necessary to start with the isolated sulfonic acids, but the same can be directly saponified in the reaction mixtures resulting from their process of manufacture.

The invention is illustrated by the following examples, without being limited thereto:

Example 1. kgs. of the sodium salt of benzoxazole-Z-sulfonic acid are dissolved in 300-400 litres of warm water, and the solution is Weakly acidified with hydrochloric acid. The Z-hydroxybenzoxazole having the following formula of the melting point 140 C. separates in a good yield with splitting off of sulfurous acid.

Example 2.-50 kgs. of the sodium salt of snaphthoxazole-Z-sulfonic acid are dissolved in about 300 litres of warm water; on acidifying the solution with sulfuric acid, sulfurous acid is split off with formation of Z-hydroxy-c-naphthoxazole of the formula:

O2N s by splitting oif sulfurous acid from the corresponding 2-sulfonic acid which intermediarily has formed. After redissolving from aqueous caustic soda lye and salting out with common salt, the sodium salt of 2-hydroxy-6-nitrobenzothiazole is obtained in form of yellowish crystals; the free compound shows the melting point 252 C.

In an analogous manner there is prepared the 2-hydroXy-5nitrobenzothiazole of the melting point 282 0.

Example 4.40 kgs. of 2-mercapto-benzothiazole are dissolved with 25 kgs. of aqueous caustic soda lye of 50% strength in 100 litres of water, and at 20-30 C. there is slowly added a solution of 80 kgs. of potassium permanganate in about 800 litres of water. After this the reaction mixture is heated to 80-90 (3., and the manganese sludge formed is filtered off. The filtrate containing the benzothiazole-Z-sulfonicacid is rendered acid to congo with hydrochloric acid, while hot, whereupon the bulk of the 2-hydroxybenzothiazole separates directly with a strong development of S02. A further quantity of the 2- hydroxybenzothiazole crystallizes on cooling. The output is about 90% of theory. The product having the following formula:

is very pure and shows the melting point of 138 C.

The process can also be performed at other temperatures between about 50 and about 100 C. In an analogous manner there are prepared from the corresponding benzothiazole-2-sulfonic acids or naphthothiazole-Z-sulfonic acids respectively: 4-chloro-2-hydroxybenzothiazole of the formula:

of the melting point 204-205" C.

5-chloro-2-hydroxybenzothiazole of the formula:

of the melting point 218 C.

6-methoxy-2-hydroxybenzothiazole of the formula o-on H300- \s of the melting point 163-164 C. 2-hydroxy-a-naphthothiazole of the formula:

of the melting point 287-288" C. 2-hydroxy-p-naphthothiazole of the formula:

ar C- S 03y wherein ar stands for an arylene radical of the benzene or naphthalene series, :0 stands for a member of the group consisting of sulfur and oxygen, and 1 stands for a member of the group consisting of hydrogen and a monovalent metallic radical, by treating with an acid saponifying agent.

2. A process as claimed in claim 1, in which a dilute aqueous mineral acid is used as saponifying agent.

3. The process of preparing 2-hydroxyoxazole which comprises treating oxazole-Z-sulfonic acid with dilute aqueous hydrochloric acid at normal temperature.

4. The process of preparing 2-hyclroxybenzothiazole which comprises treating benzothiazole- 2-sulfonic acid with dilute aqueous hydrochloric acid at a temperature between about 50 and about 100 C.

ERNST HERDIECKERHOFF. EDUARD TSCHUNKUR. 

